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Thread: CNS discussion (split from the infamous AM thread)

  1. #1
    RBW Member MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV's Avatar
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    CNS discussion (split from the infamous AM thread)

    Tino,
    first my apologies for having dug out this post of yours from some distant path. I am fully aware that you may have received competent answers yet in more recent posts which I have not read yet.
    It has been some time since I have been around here, and asíde from heaving a virus ruined my old computer, am lagging quite a bit in my reading of some of the most interesting threads here.

    On the subject of CNS algorhythms, I think you missed the point Alex made.
    1) With a linear alghorythm, like the one habitually used, and having no scientific background whatsoever, divers may stay down long enough to devellop lung symptoms, like reduced ventilation rates ( VC, PEF 25-75).
    This has been proven in scientific studies at the German Navy's Medical Institute in Kiel, by Drs. Tetzlaff and Koch e.a.
    Literally, each dive within a certain set of parameters, will show this result.

    2) You put far too much in the absolute number the familiar CNS algorhythm give, with respect to currently used warning treshold, whereas Alex focus clearly lies on the steep slope of sliding into danger of Oxtox when experiencing higher levels of CO2, whatever the "CNS-value"may be.
    Again this dependancy seems to me quite well known, from the olden days when even Narcosis was attributed to higher CO2 levels, up to the recent publications and studies done at the Kiel Institute by Dr. Andreas Koch and his colloegues.
    He represented his results at the G.T.UE.M.'s scientific meeting in Heidelberg this spring, where he also presenting the time/pp dependancy of the onset of Oxtox symptoms as well as the new found method of detecting in good time to be able to counteract.
    Cheers,
    Matthias


    Quote Originally Posted by Tino de Rijk  View Original Post
    Alex,
    ..I think it is important, because if YOU are right, Andrew will have to re-visit his pending paper, and I will have to go back to my medical committee.
    On the other hand, if you cannot convince us with hard proof, I expect you to re-assess the "clear links" you state there are between CNS exceeding and diver deaths in your list, especially as it is now being used in court as evidence.
    We don't want the wrong conclusions being drawn and reported, do we...?


    ciao,

    Tino.

  2. #2
    RBW Member MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV's Avatar
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    Re: Comprehensive list of all accidents

    Hi Dave,

    hope the little Draeger helped a bit.
    I still always have some with me, when diving, unless I have to use airlines to get there.
    10 years sealed, w/o service, no problem. When I had a little DCS event last year, I breathed from one for an hour, and even fell asleep some time (kids, don't do that at home!)

    Best,
    Matthias


    Quote Originally Posted by Dave ******  View Original Post

    Photos of the unit under test as a teaser. And yes, with repackaging and use of lime rather than the Lithium scrubber it'll be modifiable to work as a bail out rebreather: Carried in an aluminum case sealed at 1 ATMA and being able to be deployed at depth and placed into service in about 30 seconds from the sealed state. It's a disposable rig (factory serviced after use) and is designed to be carried for 5 years between inspections, and has been tested to 2+ hours using Lithium scrubber. We need to get it finished as a mine escape system before putting attention to the diving market. What is shown is just a very rough prototype: NDA prevents posting the further developments.
    .

  3. #3
    RBW Member MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV's Avatar
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    Re: Comprehensive list of all accidents

    Hi Alex,

    [quote=AD_ward9;191475]


    > There is also an anomaly that sine flow rather than sine pressure drive is >used in the current WOB definitions.

    I am very glad that you point at that.
    There is a considerable crest factor between sinoid and actual breathing.
    The mean peak flow rate (SAC) in competition diving I did once, was 130l/min. From my physicals I know my peak inspiriatory flow to be more than 300 l/min.
    Any device not offering this flow with ease, when it really counts, will give the diver a feeling of suffocation.

    cheers,
    Matthias

  4. #4
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    Re: CNS exposure and RB deaths in list

    Quote Originally Posted by MatV  View Original Post
    Tino,
    first my apologies for having dug out this post of yours from some distant path. I am fully aware that you may have received competent answers yet in more recent posts which I have not read yet.
    It has been some time since I have been around here, and asíde from heaving a virus ruined my old computer, am lagging quite a bit in my reading of some of the most interesting threads here.

    On the subject of CNS algorhythms, I think you missed the point Alex made.
    1) With a linear alghorythm, like the one habitually used, and having no scientific background whatsoever, divers may stay down long enough to devellop lung symptoms, like reduced ventilation rates ( VC, PEF 25-75).
    This has been proven in scientific studies at the German Navy's Medical Institute in Kiel, by Drs. Tetzlaff and Koch e.a.
    Literally, each dive within a certain set of parameters, will show this result.

    2) You put far too much in the absolute number the familiar CNS algorhythm give, with respect to currently used warning treshold, whereas Alex focus clearly lies on the steep slope of sliding into danger of Oxtox when experiencing higher levels of CO2, whatever the "CNS-value"may be.
    Again this dependancy seems to me quite well known, from the olden days when even Narcosis was attributed to higher CO2 levels, up to the recent publications and studies done at the Kiel Institute by Dr. Andreas Koch and his colloegues.
    He represented his results at the G.T.UE.M.'s scientific meeting in Heidelberg this spring, where he also presenting the time/pp dependancy of the onset of Oxtox symptoms as well as the new found method of detecting in good time to be able to counteract.
    Cheers,
    Matthias
    Dear Matthias,

    Thanks for the answer. It is never too late for a good reply.
    I think you in turn mis-interpret my answer.
    As to point #1: we do not disagree on that one, but what you describe is general considered and described as "pulmonary toxicity", which has its own sets of toxicity rules, expressed in OTU/UPTD. It is indeed "marked" by measureable rediction on VC. I do not dispute those at all, and we still apply those in full (i.e. UPTD counting). There is very much (also non-diving related) info and "proof" as to its existence and onset and symptoms and treatment.
    It has however not a lot to do with CNS toxicity, i.e. the typical neurological symptoms from the CONVENTID symptoms scheme. What it at best shares is the root-cause "free radicals" theory as the foundation for the damage - but even that theory is disputed (at least for CNS).

    as to point #2: we do not disagree again. In fact, my statement was, overly simplified: the "hard" use of CNS tables (e.g. "do not exceed 45 minutes at a PO2 of 1.6, or 180 minutes at 1.3") have little or no valid, good peer-researched scientific foundation. It creates a false sense of safety, especially at higher PO2's (e.g. divers reasoning "so 44 minutes at a PO2 of 1.6 is o.k. and will not cause an tonic-clonic insult"). It is much safer to advise to stay away from high PO2's, e.g. consider 1.3 as maximum PO2, because above that your risk at CNS symptoms increases, BUT it cannot be reliable modelled and put into a reilable exposure table.

    This is the key-statement: you cannot RELIABLE model it.

    So we dropped those CNS time/exposure tables, and replaced them with a simple "do not exceed a PO2 of 1.4" rule. Notice also this is in the context of renewing an Open circuit Advanced Nitrox course, not a Rebreather course. In RB's the limit should possible be even lower due to the increased potential additional risk factor of CO2 buildup.

    One final remark: the fact that one very credible research institute (in this case Heidelberg) has taken up a position in this is unfortunately not enough for me. The problem with the very mixed message around CNS intoxication and its tables is exactly caused by the fact that very credible researchers and research institutes over the world have done in itself interesting studies, but few if any have undergone the these days mandatory "peer review" concept and have seen a sufficiently enough big testgroup (and counter-test group) to be scientifically valid and "generally accepted" enough.
    Also very good researchers have vested opinions, and are not always right, and/or research for a specific target group (e.g. military divers - generally better screened and fitter, different work patterns and dive profiles).

    Ciao,

    tino.

  5. #5
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    Re: CNS exposure and RB deaths in list

    hi Tino,

    [quote=Tino de Rijk;216382]Dear Matthias,

    Thanks for the answer. It is never too late for a good reply.
    I think you in turn mis-interpret my answer.
    As to point #1: we do not disagree on that one, but what you describe is general considered and described as "pulmonary toxicity", which has its own sets of toxicity rules, expressed in OTU/UPTD. It is indeed "marked" by measureable rediction on VC. I do not dispute those at all, and we still apply those in full (i.e. UPTD counting). There is very much (also non-diving related) info and "proof" as to its existence and onset and symptoms and treatment.

    MV:
    __No Doubt. Still only short times far from accounting for any significant rise in UPTDs of breathing elevated pressures of oxygen reduce vital capacity and lead to the swelling of vessel walls in lungs and arteriolae. While this is noway a synonym for the onset, or even an elevated susceptibilty for oxtox, it is undesirable becuase it interferes with proper decompression. Hence the need for backgas breaks.
    To give sa number taken in a controlled environment ( chamber rides), I can feel this constriction set in after 17 minutes on a ppO2 of 2,4 bar, which is completely reversed after an appropiate airbreak at same ambient pressure.


    T:
    It has however not a lot to do with CNS toxicity, i.e. the typical neurological symptoms from the CONVENTID symptoms scheme. What it at best shares is the root-cause "free radicals" theory as the foundation for the damage - but even that theory is disputed (at least for CNS).
    ...
    So we dropped those CNS time/exposure tables, and replaced them with a simple "do not exceed a PO2 of 1.4" rule. Notice also this is in the context of renewing an Open circuit Advanced Nitrox course, not a Rebreather course. In Rebreather's the limit should possible be even lower due to the increased potential additional risk factor of CO2 buildup.

    MV:
    Absolutely. The tendency goes to even more reduced levels, like 0,8-1 bar.



    T:
    One final remark: the fact that one very credible research institute (in this case Heidelberg) has taken up a position in this is unfortunately not enough for me.

    MV: Sorry for not having been clear enough. Dr. Andreas Koch at the moment probably the most experienced expert on Oxtox in this area. His research is well peer reviewed, and even has been granted a full time job for a chemist of Fraunhofer society.

    Heidelberg was the place where this years GTÜM's international scientific meeting took place, where I not only had the great pleasure to take part in, but also have a M.S in chemistry at my side, which most of the physicians at this place did not (what might have made it hard to follow Andreas' presentation. He is based in the "Schiffahrtssmedizinisches Institut der Marine" in Kiel.

    To answer any further questions ( rather to make them rise , here is a link to the presentation, held at a Bonn Symposium. Hope you understand some german, though Bubblefish would probably an interiesting reading...

    Salve,
    Matthias

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    Re: Comprehensive list of all accidents

    Hi Tino and Matthias,

    This discussion is fascinating and could, if I'm reading you right, point to one of the underlying causes of higher apparent mortality rates amongst CCR divers. That deserves it's own thread IMHO.

    Dear Mods,

    If you agree, could you split the posts on this topic (I think starting with Matthias' first post yesterday) from this thread and into a new one?

    Thanks all!

    Cheers,

  7. #7
    RBW Member MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV's Avatar
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    Re: CNS exposure and RB deaths in list

    Oops,
    ....
    To answer any further questions ( rather to make them rise , here is a link to the presentation, held at a Bonn Symposium. Hope you understand some german, though Bubblefish would probably an interiesting reading...

    Salve,

    here is the link. Remeber to fully copy the lines.
    Matthias

    http://www.bonner-tauchersymposium.d...sache_2008.pdf

  8. #8
    RBW Member MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV's Avatar
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    Re: Comprehensive list of all accidents

    Alex, or others,

    Just a question, regarding incidents where the sensor display or values were questionable:

    Could it be traced somehow, if, at the moment of calibrating, there had been anybody around using a cell phone, or, on a ship, there had been the possibility to have been situated within the reach of a working radar or it's near reflection?

    A calibrating process done by digital code may be prone to be disturbed by electromagnetic radiation, whereas by trimpots most probably not.

    cheers,
    Matthias

  9. #9
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    Re: CNS exposure and RB deaths in list

    Quote Originally Posted by MatV  View Original Post
    Oops,
    ....
    To answer any further questions ( rather to make them rise , here is a link to the presentation, held at a Bonn Symposium. Hope you understand some german, though Bubblefish would probably an interiesting reading...

    Salve,

    here is the link. Remeber to fully copy the lines.
    Matthias

    http://www.bonner-tauchersymposium.d...sache_2008.pdf
    Thanks, Matthias.
    and yes, my German is good enough to read it without problems (one of the few advantages of being Dutch: no-one speaks Dutch, so we have to learn other languages, especially those of our close neighbours....). I have read the article (as it is only two pages) and I agree with it all.

    I did in no way intend to discredit anyone. It is just that much research in the medical area is not properly peer-reviewed, and lots of research contradicts each other. I am lucky to say that I have good contacts with a.o. Andrew Gasman (who is also present here on RBW) and David Sawatzky (ex DCIEM/DRDC), both also quite renowned medical hyperbaric specialists. The (ex-)chairman of the medical committee I have been referring to is Dr. Rob van Hulst, a good friend and also for many years now the chief of the Dutch Royal Navy's Dive Medical Center (DMC) in Den Helder, Holland. Amongst the committe members are a.o. a quite reknowned university neurologist (Dr. Gerhard Visser) and cardiologists.
    In fact, reference # 8 in the article link you sent me refers to an article by Rob van Hulst and Gerhard Visser - no coincedence! They did (promotion) research on what happens in the brain when exposed to high PO2. They researched that "in vitro", by implanting advanced multi-sensing electrodes into the brain of a live (sedated) pig and then putting that pig into a deco chamber with various PO2's and deco profiles.

    So my "back-up" is quite strong. That is important if you are writing about medical stuff in e.g. training manuals without being medical trained yourself, like me. But you learn a lot along the way, by talking with those guys...!

    You talk about a presentation, but the link you provide is to a 2-page article.
    Is there more...?

    Ciao,

    Tino.
    Last edited by Tino de Rijk; 17th October 2008 at 15:26. Reason: typo's

  10. #10
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    Re: CNS exposure and RB deaths in list

    Hi Tino,
    Quote Originally Posted by Tino de Rijk  View Original Post
    .........
    In fact, reference # 8 in the article link you sent me refers to an article by Rob van Hulst and Gerhard Visser - no coincedence! They did (promotion) research on what happens in the brain when exposed to high PO2. They researched that "in vitro", by implanting advanced multi-sensing electrodes into the brain of a live (sedated) pig and then putting that pig into a deco chamber with various PO2's and deco profiles.

    MV: Yep. Some use pigs, other goats, other used snakes, other volunteering convicts...
    Think we need some kind of canary bird within the loop, like in old day's mines.


    Tino:
    You talk about a presentation, but the link you provide is to a 2-page article.
    Is there more...?

    Tino.
    There is. Some of it is not yet published. There were several doctorate thesis involved in this study group.
    Amongs else, they found a way of detecting oxygen stress in divers and non divers ( athletes), e.g. stress from exposure to high levels of oxygen,, high ambient pressure, exertion, combination thereof, by testing urine samples with expensive machinery, which looked like chromatographic equipment to me.

    I tried to link Andreas to JJ, to speak at the GUE World conference in Budapest last winter, but maybe his expertise is to special for the general GUE set of themes. At least they are aware that we've already got electric lighting in Europe

    Rob Bakker in Norway is working on the same subject, he found ways to detect oxygen stress by blood sampling.

    I understood most of this will be published in full in medical Journals, not in Dive Mags.
    On some subjects, peer review is still going on.

    Cheers,
    Matthias

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